This invention relates to monovinylidene aromatic polymer resins more particularly coupling such resins.
In general, the basic physical properties that are usually desired in the production of molded thermoplastic resin articles are an easily processable starting resin which produces articles that are relatively strong and heat resistant. It is within the skill in the art to produce relatively strong, heat resistant articles from monovinylidene aromatic polymer resins. Most resins used in producing articles possessing these properties must be modified in some way to improve their melt flow characteristics enough to allow them to be both easily and rapidly processed on available processing equipment, such as injection molding equipment, under normal conditions.
To avoid extended residence time requirements and the consequent equipment requirements, it would be desirable to polymerize vinyl aromatic monomers to a lower molecular weight and subsequently build the low molecular weight polymers to higher molecular weight polymers.
It would also be desirable to use lower molecular weight vinyl aromatic polymers for processability and to subsequently build molecular weight to enhance melt strength and extensional properties of a foam stock. Increasing the molecular weight would preferably also increase cell size or density or both. More preferably, by treating the polymer starting materials, one could achieve at least one of greater throughput of polymer into foam (e.g. in kilograms per hour) or lower density than with untreated starting material in the same foaming process while retaining of equivalent or better crush strength or flexibility or both.
In the past, difunctional sulfonyl azides have been used to bridge such polymers as polypropylene, for instance as disclosed by Cox et al. in U.S. Pat. No. 3,336,268, but such reactions lead to crosslinking. Thus, the reactions might be expected to have adverse effects on foams or other properties of vinyl aromatic polymers.